1. Technical Field
This invention relates generally to the field of subsurface reservoir communication with a wellbore.
2. Description of Related Art
To complete a well, one or more subsurface formation zones adjacent a wellbore are perforated to allow gaseous and liquid hydrocarbons from the formation zones to flow into the well for production to the surface or to allow injection fluids to be applied into the formation zones. A perforating gun string may be lowered into the well and the guns fired to penetrate metal casing, cement, or other materials in the wellbore, and to extend perforations into the surrounding formation.
The explosive nature of the penetration of perforation tunnels comminutes the adjacent rock, fractures sand grains, dislodges intergrain cementation, and debonds clay particles, resulting in a low-permeability “shock damaged region” surrounding the tunnels. The process may also generate a tunnel full of rock debris mixed in with the perforator charge debris. FIG. 1 shows a typical perforation tunnel created in a subsurface formation. The wellbore 10 is shown including casing 12 and a layer of cement 14. A shock damaged region 16 surrounds the perforation tunnel 18. The extent of the damage, and the amount of loose debris in the tunnel, may be dictated by a variety of factors including formation properties, explosive charge properties, pressure conditions, fluid properties, and so forth. The shock damaged region 16 and loose debris in the perforation tunnels negatively impacts hydrocarbon production.
One popular method of obtaining cleaner perforations is underbalanced perforating. The perforation is carried out with a lower wellbore pressure than the formation pressure. Underbalanced perforating and wellbore pressure control techniques are described in D. Minto et al., Dynamic Underbalanced Perforating System Increases Productivity and Reduces Cost in East Kalimantan Gas Field: A Case Study, SPE/IADC 97363 (2005); Eelco Bakker et al., The New Dynamics of Underbalanced Perforating, OILFIELD REVIEW, Winter 2003/2004, at 54; and U.S. Pat. Nos. 7,243,725, 4,605,074, 6,527,050, 4,903,775. Though advances have been made, conventional perforation techniques remain limited by the reservoir pressure and relatively ineffective in low-pressure reservoirs.
A need remains for techniques to improve reservoir communication with wells in subsurface formations.